If a 5 year old is knocking on your door at 9:30pm at night in a neighborhood that sounds unsafe (though what neighborhood is safe at 9:30pm at night for a 5 year old, all alone without parental supervision?)..it seems you should call child services and have a social worker go out to the house. Make sure it is anonymous so that you do not put yourself or your children at risk for revenge from your neighbor (the father, in particular, if you think he's in a gang.). This little boy could have been snatched by a stranger if he's out at that hour without his parents even paying any attention. Also, if he's 5 he should be in school, not at home all day with his parents. And it goes without saying that he should be fed regularly, also by his parents. There are plenty of food programs that are very easy to get onto for a parent who has little or no income, and food stamps, WIC coupons (WIC stands for WOMEN INFANTS CHILDREN and it's a state run program for women with children who need help getting food for their kids.)...there is NO EXCUSE for this child not getting food.
Call social services. You could save a life.